This invention relates to a method for using water-soluble organotitanium(IV) compounds to control pitch deposition in pulping and papermaking processes. One aspect of this invention pertains to a method for preventing the deposition of pitch on machinery used in pulping and papermaking processes. Another aspect of this invention pertains to a method of preventing the formation of visible pitch particles in the final paper of a papermaking process. Yet another aspect of this invention pertains to a method for removing pitch deposits from machinery used in pulping and papermaking processes.
The problems caused by the build-up of pitch on pulping and papermaking machinery and in the final paper costs the pulp and paper industry more than 30 million dollars a year in lost production. Pitch is generally considered to be a resin based deposit of widely varying composition originating in the extractive fraction of wood. The extractive fraction of wood is one of the four principal components of wood. The other three are cellulose, lignin and hemicellulose. The extractive fraction is defined as a complex mixture of substances which are soluble in cold water, alcohol, benzene, ether and acetone. The extractive fraction, Which makes up from about 3% to 10% of the weight of wood, contains such components as low molecular weight carbohydrates, terpenes, aromatic and aliphatic acids, alcohols, tannins, color substances, proteins, phlobaphens, lignins, alkaloids and soluble lignins. Pitch is a major problem in pulp and papermaking because it (1) agglomerates and occludes other matter to form visible "dirt" in the final paper, (2) plates out and collects on machinery used in pulping and papermaking process such as screens, filters, refining equipment, pulp washers, and the paper machine, and (3) reduces pulp brightness and brightness stability.
The composition and amount of pitch deposited on pulping and papermaking machinery and in the final paper varies with the time of the year the trees are harvested, the type of wood and the type of the pulping process. For example, wood pulped from trees cut in the early spring and fall causes more pitch problems than wood from trees cut at other times during the year. Pitch deposited in softwood Kraft mills tends to have a relatively larger abietic acid to fatty acid ester ratio than pitch found in hardwood Kraft mills. Pitch deposit problems are somewhat more severe in sulfite mills. The sulfite pulping process removes only about one half of the resins and fatty acid esters, thus leaving a considerable portion of these materials encapsulated within the cellulose fibers. However, these encapsulated materials are released by the shearing forces of the refining process and thus pitch deposits are more prevalent in the stock preparation area and on the paper machine. Pitch problems can be quite bothersome in mechanical pulp mills, including groundwood, thermomechanical, chemical thermomechanical and semi-chemical pulping processes, particularly those that utilize softwoods. This is because there is little chemical degradation of the fatty acid esters and resin esters. Therefore, those materials are not washed out and tend to remain dispersed in the aqueous system of the pulping process.
The presence of calcium carbonate in the pulping process exacerbates the problem of pitch deposition on pulping and papermaking machinery. Crystallized calcium carbonate can provide nucleation sites for precipitated metal soaps, thereby producing hydrophobic particles which coalesce with other particles to form a pitch deposit.
There have been many attempts over the years to eliminate pitch problems by employing pitch control agents in the pulping and/or papermaking processes. The most common methods involve the use of alum, talc, anionic pitch-control agents such as polynaphthalene sulfonates or modified lignosulfonates, cationic pitch control agents such as polyquaternary ammonium polymers and nonionic surfactants. An example of the use of polyquaternary ammonium polymers as pitch control agents can be found in U.S. Pat. No. 2,582,461. The patent discloses the use of water soluble dicyandiamideformaldehyde condensates to prevent pitch deposition on machinery used in pulping and papermaking processes. Examples of attempts to control pitch with other types of compounds or processes are found in U.S. Pat. Nos. 3,812,055, 3,895,164, 3,896,046, 3,992,249 and 4,313,790. None of the above methods or compositions is completely effective in preventing pitch from depositing on machinery used in the pulping and papermaking processes. None of the above methods or compositions is completely effective in preventing pitch from depositing in the final paper produced in the pulping and papermaking processes. None of the above methods or compositions is effective at all in removing pitch deposits from machinery used in the pulping and papermaking processes during the operation of these processes. Pitch deposits are normally removed from the machinery used in the pulping and papermaking processes during shut down periods when the machinery is not in actual operation.
Recently, the use of water soluble zirconium salts to control pitch deposition and remove existing deposits has been reported (U.S. Pat. No. 4,950,361). This patent discloses a method of removing pitch deposits from machinery used in the pulping and papermaking processes while the machinery is in operation. The method disclosed in the patent also prevents pitch deposition on the machinery and in the final paper product.
Organotitanium chemicals have been used by the paper industry since the late 1950s, principally for use in crosslinking organopolysiloxanes used in rendering paper and cardboard surfaces more hydrophobic, thereby improving ink acceptance. Examples of such use can be found in U.S. Pat. No. 3,058,936 and Finland Patent No. 175,340. Cellulose treated with triethanolamine titanate has been reported to exhibit a considerably higher wet strength than that from untitanated pulp. The titanic acid resulting from aqueous solutions of triethanolamine titanate was reported to be the active compound for obtaining improved wet strength and ink acceptance properties with paper. (Anorg. Alg. Chem., 403, 337 (1974)).